The present invention relates to a new anchoring system.
The anchoring system according to the invention is in particular, suitable for securing in position floating structures such as chips, offshore drilling and hydrocarbon production platforms, etc. This anchoring system is also suitable for anchoring structures on land.
Conventional anchoring system of positioning a plate, or hook in the ground, to which a horizontal pull is subsequently applied by means of a rigid rod or shank connected to a chain by means of an eyelet.
The weight of this anchor is high so as to permit the initial penetration of the flukes or hooks into the ground, this penetration being only slight when the anchor is just laid onto the ground and subsequently increasing as the anchor is dragged. Ahead of the buried fluke of the anchor, the ground acts as an abutment and a wedge similar to the Coulomb's wedge is formed: the anchor and the ground wedge would have a tendency to glide upwardly in the absence of the anchor weight which maintains the anchor fluke or flukes buried at a certain depth, thus providing for a kinematic equilibrium, so that it is often assumed that the holding power of an anchor, (i.e. the highest admissible horizontal pull F), is proportional to the anchor weight P. Depending on the anchor shape, the ratio (F/P) comprises a value of between 5 and 15 for a sandy water bottom, and between 8 and 20 for a clayish bottom.
Thus high capacity anchors are very heavy, weighing up to 10 or 15 tons.
An additional requirement is that the anchor must always be positioned correctly for gripping the ground when it is laid, irrespective of the configuration of the water bottom. This has lead to anchor shapes generally having two planes of symmetry, such as the very conventional and well known grapnel type anchor or anchors having hinged mechanisms allowing pivoting about a shaft at the end of the anchor shank and perpendicular thereto, such mechanisms providing for symmetrical positions of the anchor.
Moreover, since the anchor must be weighed at the end of the mooring period, additional devices are sometimes used to facilitate this operation.